The proposal deals with very early development of peripheral and central taste systems in the rat. Three of the specific aims build on the principal investigator's demonstration that taste papillae will form in vitro from organ cultures of the embryonic rat tongue lacking normal sensory innervation. Specific Aim 1 will determine the potential for development in organ culture as a function of the age of the embryonic tissue. It will attempt to establish embryo age thresholds and cut- offs. Specific Aim 2 determines if in vivo molecular characteristics of tongue are maintained in organ culture. Aim 3 determines the effects of co-culturing the tongue with gustatory and nongustatory sensory ganglia on papilla and taste-bud formation in vitro. Specific aims 4 nd 5 deal with second order taste neuron development and utilize brainstem slices of the NST to explore basic changes in neuron circuitry and function. Specific Aim 4 tests the hypothesis that the adult level of sensitivity of NST neurons to excitatory and inhibitory neurotransmitters is acquired gradually following birth. Aim 5 tests the hypothesis that intrinsic neurotransmitter characteristics of rat NST cells are altered by dietary sodium deprivation. These in vitro systems have not previously been used to study development in taste, a sense that influences food selection and nutrition.